The present invention relates to methods and apparatus for deep water plug and abandonment systems used on the mineral production industry. Prior art systems typically require at least four (4) trips to the wellhead to cut and retrieve casing for abandonment of the well. In the first trip, the wear bushing is pulled. In the second trip, a device is used to engage the seal assembly and pull the seal assembly to the surface. In the third trip, a device is used to engage a spear to grip the casing, a cut is made in the casing with a rotary driven cutter, the top portion of the cut casing is pulled up through the riser. In the fourth trip, cement plugs are set for isolation.
Several systems for cutting and pulling the casing and well head to the surface of the water are known in the industry. The following are a few examples.
U.S. Pat. No. 3,983,936, herein incorporated by reference, discloses a method of and apparatus for cutting and recovering submarine surface casing and associated equipment on the ocean floor. It includes the steps of lowering a string into the surface casing which string includes a swivel, a spear and a cutter, seating the swivel on the casing well head seat, actuating the cutter to sever the casing, setting the spear within the casing and recovering the surface casing and well head equipment associated therewith.
U.S. Pat. No. 4,703,802, herein incorporated by reference, discloses a cutting and recovery tool for a well-head, having a housing which is adapted to engage with a side wall of the wellhead to lock them together, and a mandrel extending through the housing and rotatable relative to the housing and adapted to carry a radially-acting cutter which severs the wellhead below the area of engagement of the housing. This allows the wellhead to be severed and withdrawn in a single operation.
U.S. Patent No. 4,550,781, incorporated herein by reference, discloses a method of cutting and retrieving submarine well casing which includes the steps of lowering a tool on a string into the bore of the well casing which tool includes a casing cutter, a bumper sub connecting from the cutter to the combined anchor swivel and latching means to retain the anchor in unset position when it is being run with the string connected to the upper end of the tool, landing the tool with the swivel supported on the upper end of the casing and the remainder of the tool within the casing, releasing the latching means, raising the string to set the anchor, tensioning the string, energizing the cutter arms, rotating the string to cut the casing, and raising the string to retrieve the cut casing. The apparatus includes a casing cutter, a bumper sub, a combined anchor swivel and latching means to retain the anchor in unset position which latching means is actuated to unlatched position by manipulation of the string on which the tool is supported.
U.S. Pat. No. 4,144,936, incorporated herein by reference discloses an apparatus for milling metal submerged in salt water or within a hole, such as cutting off the upper ends of pipes and casings in a well-drilling operation below the sea floor. A hydraulic motor is suspended in the hole and driven by sea water to rotate an electrical generator and to rotate a cutting tool. The tool includes radially movable, electrically conductive elements which form the cathodes of an electrochemical machining operation for removing metal. The tool elements include abrasive material so that they can mechanically cut through cement.
U.S. Pat. No. 5,318,115, incorporated herein by reference, discloses a casing cutting and retrieving tool is described which includes a grapple device for mechanically gripping casing to be retrieved. A mud motor having upper and lower stators and a rotor is also provided. The upper stator acts as a suspension device for suspending the grapple device from a drill string, and the upper stator is mechanically fast with the grapple device. A rotary cutter depends from a drive end of the rotor and is rotatable by the rotor to cut the casing at a location below the grapple device.
However, in all prior art systems it is necessary to make a separate trip with the working string to engage the seal assembly in the wellhead and pull the seal assembly to the surface. This trip, like all trips, requires time and money. Therefore, there is a need for a plug and abandonment system which does not require a separate trip to pull the seal assembly from the wellhead.
The present invention provides a seal assembly retrieval device which is incorporated with casing cutter and spear devices to create a system which does not require a separate trip to pull the seal assembly.
According to one aspect of the invention there is provided a well abandonment process for cutting and retrieving an offshore well casing, the process comprising: making a trip to the well wherein all of the following steps are performed, the steps comprising: pulling a seal assembly from the wellhead, cutting the casing, griping the casing, and retrieving the seal assembly and cut casing.
According to another aspect of the invention, there is provided an apparatus for cutting and retrieving an offshore well casing, the apparatus comprising: a seal assembly retrieval tool for releasing a seal assembly of the well casing, wherein the seal assembly retrieval tool is connectable to a drill string for suspension from the drill string; a spear in mechanical communication with the seal assembly retrieval tool, wherein the spear is engageable with the well casing; a mud motor in mechanical communication with the spear; and a casing cutter in mechanical communication with the mud motor, wherein the casing cutter is driven by the mud motor to cut the well casing.
According to still another aspect of the invention, there is provided an apparatus for cutting and retrieving an offshore well casing, the apparatus comprising: a seal assembly retrieval tool for releasing a seal assembly of the well casing, wherein the seal assembly retrieval tool is connectable to a drill string for suspension from the drill string; a first bumper jar in mechanical communication with the seal assembly retrieval tool; a spear in mechanical communication with the first bumper jar, wherein the spear is engageable with the well casing; a second bumper jar in mechanical communication with the spear; a mud motor in mechanical communication with the second bumper jar; and a casing cutter in mechanical communication with the mud motor, wherein the casing cutter is driven by the mud motor to cut the well casing.
In some embodiments of the invention, it is preferred to cut the casing while the casing is under tension. Since the spear is engaged with the casing before the casing is cut, the operator may lift up on the tool so as to induce an upward force on the casing. This action takes the weight of the casing off the portion of the casing being cut.